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Nanoscale phase separations, and effects of these, were studied for thick super duplex stainless steel products by atom probe tomography and mechanical testing. Although nanoscale phase separations typically occur during long-time service at intermediate temperatures (300–500° C, our results show that slowly cooled products start to develop Fe and Cr separation and/or precipitation of Cu-rich particles already during fabrication. Copper significantly slowed down the kinetics at the expense of Cu-rich particle precipitation, where the high-copper material subjected to hot isostatic pressing (HIP), with Δt500–400 of 160 s and the low-copper hot-rolled plate with Δt500–400 of 2 s had the same level of Fe and Cr separation. The phase separations resulted in lower toughness and higher hardness of the HIP material than for hot-rolled plate. Therefore, both local cooling rate dependent and alloy composition governed variations of phase separations can be expected in as-fabricated condition.

Polyaniline (PANI) electrodeposition on bare and carbon nanotube (CNT) coated 316 SS was carried out using a cyclic voltammetry (CV) electropolymerization method in diluted H2SO4 media containing aniline monomer. CNTs were grown in a thermal CVD reactor on 316 SS either by direct growth using ethylene precursor or by continuous feeding of an external catalyst, ferrocene, dissolved in toluene as the carbon precursor. Corrosion behavior of the coated materials was assessed by potentiodynamic and potentiostatic methods in an attempt to simulate the working conditions of proton exchange membrane fuel cell (PEMFC) bipolar plates. While a thick PANI coating could not provide a protective barrier to either bare or CNT coated 316 SS samples, a sensible improvement in corrosion resistance was revealed in the presence of a thin PANI layer. However, the protective capability of the PANI thin film was still inadequate for the purpose of providing reasonable corrosion resistance to the material under simulated PEMFC conditions, due to severe deterioration of CNT coated 316 SS caused by the initial carbon treatment.

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